Coolant loss through overflow tube?

'90 Maxima…I’ve noticed coolant reservoir has been running low/dry and I also notice coolant dripping from the overflow hose. Why would it keep pushing more coolant out if there isn’t an excess in the reservoir? Engine runs fine., no other issues.

It could be a few different things but the most common one is a bad radiator cap. The next thing to look for is a thermostat that’s sticking in the closed position. My money is on the radiator cap.

Where is the leak, exactly? The tube that connects the overflow tank to the radiator or the overflow from the tank itself? How can the tank overflow if it’s low / empty?

I’ll agree with missileman. Radiator cap would be the first thing to replace.

Then check the coolant level in both the radiator and the reservior.


If your overflow reservoir is the type with both the tube from the radiator and the overflow tube attached, then the two tubes have been switched.

Another possibility - head gasket. But that’s after eliminating all the other cooling system problem possibilities.

When you refill the reservoir, how long does it take to empty?

Overheating, from any number of possible causes. If you’re lucky, you may just need a new radiator. If the shroud can be moved back, a mechanic can look at the fins. If about 5% of them are rotted away, the radiator should be replaced.

The way the system works is simple. The radiator cap allows the pressure to build inside the engine as the coolant heats up until it reaches about 15-16 pounds (a typical cap rating). Since pressurized fluid boils at a higher temperature than room temperature fluid, that allows the system to operate a higher temperatures without boiling over.

When the pressure exceeds the cap pressure rating, some fluid is allowed past the radiator cap and flows into the reservoir. Then, when the fluid cools and contracts at the end of the day, the cap allows the coolant in the reservoire to freely flow back into the engine, keeping the system full even after the fluid has contracted.

The level in the reservoir will rise and fall as the coolant heats up and cools down. If the reservoir is filled too full, excess will blow out the overflow tube when the coolant heats and expands.

Assuming that you’re not filling the reservoire beyond the “cold” fill line when cold or the “hot” fill lline when hot, then the cause of the overflowing is either overheating of the fluid or combustion gasses being blown into the water jacket, adding excess to the volume the system is trying to contain and heating up the coolant. This type of problem brings also overheating engines and operatinng problems, so I’m goin gto assume that isn’t happening, being as there’s no suggestion of operating problems in your post.

The only likely causes left are

  1. a radiator cap not holding sufficient pressure, thus allowing too much of the expanded coolant to push out into the reservoir,
  2. a stick thermostat that’s allowing the engine to run too hot and push too much coolant into the reservoire,
  3. a possible problem with the cooling system elsewhere, such as a partially clogged radiator, that’s allowing the engine to run hotter than it should.

Considering the car’s age, I’d be inclined to change the radiator cap and the thermostat. And put fresh fluid in there. 23 years is enough.

Post back and let us know if this works.

The OP never mentioned any overheating…

Thank you everyone for your posts…The car is NOT over-heating at all, and the hoses are hooked up correctly to the reservoir tank. I agree with your general consensus to change the radiator cap, perhaps the excess pressure is whats pushing all the coolant out of the reservoir. BTW, i replaced the thermostat about 20k miles ago.

If you continue to have problems with a new cap I’d have the cooling system pressure tested. Easy to do, will tell you whether you have a leak somewhere.

Got the new cap on today…hopefully that does the trick.

Also, make sure the rubber hoses connecting to th overflow tank are not cracked or leaking. Pull them off, hold your thumb over one end, and pressurize each one. Do they hold pressure? On a 90, if these are the original hoses, it wouldn’t be unusual that they are degraded and cracked, and to need new ones.

I would replace the cap first and if that isn’t the problem, then I would check for a blown head gasket.